It’s a common urban legend: a mother lifts up a car to save her screaming child pinned underneath. And every now and then, this incredible feat of “hysterical strength” seems to really happen.

In 2012, Lauren Kornacki, a 22-year-old woman in Glen Allen, Virginia, raised a BMW 525i off her father when the car toppled from a jack. Seven years earlier, a man named Tom Boylehoisted a Chevy Camaro, freeing a trapped cyclist in Tucson, Arizona. The events don’t always involve vehicles, like when Lydia Angyiou went toe-to-toe with a polar bear in northern Quebec to protect her son and his friends while they played hockey.

Scientists have only a tentative understanding of what exactly might be behind hysterical strength

Riveting as these accounts are, scientists have only a tentative understanding of what exactly might be behind hysterical strength. After all, the spontaneous, life-and-death situations that apparently unleash it do not lend themselves to rigorous study.

“You can’t really design an experiment to do this in a lab and make people think they’re going to die,” says E Paul Zehr, a professor of neuroscience and kinesiology at the University of Victoria in British Columbia, Canada. “Something has to happen by fluke.”

Nevertheless, numerous lines of research, particularly on athletes, have given us compelling insights into the physiological and psychological elements of hysterical strength. “Clearly, we have it in us,” says Robert Girandola, an associate professor of kinesiology at the University of Southern California. “It’s not some supernatural force that’s causing that strength.”

Super human, not superhuman

Before delving further, let’s establish a key point about hysterical strength: the amounts of mass often claimed to be involved in the events are less than reported.

Take the archetypal car-lifting example. A person exhibiting hysterical strength is reckoned to have lifted at least 3000lbs (or about a tonne and a half) – the ballpark weight of a mass-market, non-truck, passenger vehicle. This kind of lift is essentially a “dead lift,” where someone crouches down and then lifts an object, like a barbell with a bunch of weights on it, completely off the floor.

Could everyday folk really heft three times the world record?

The world record for deadlifting, however, stands at a mere 1,155lbs (524kg), held by Zydrunas Savickas, four-time winner of the World’s Strongest Man competition. Could everyday folk really heft three times the world record?

Probably not. Most reported hysterical strength examples describe a person lifting a portion of a vehicle several inches off the ground, and not an entire automobile. There’s the catch: three of the vehicle’s wheels – or maybe even all four, depending on the suspension – remain on the ground, distributing the total weight of the vehicle. Furthermore, a vehicle’s mass is not apportioned evenly; the heaviest part is the engine block, at the front-centre, not at the periphery where the lifting is taking place.